Historical participation by women in science and technology has been persistent but with inconsistent patterns because of the social, economic, and intellectual obstacles that have stood in their way. This account of women's initiatives and successes in 20th-century United States begins with early 20th-century involvement and suggests the subsequent ways in which the inroads of that period have influenced later struggles and strategies. Women of distinction like Marie Curie, Anna Botsford Comstock, and Ellen Swallow Richards established possibilities but also standards of exceptionalism. Data suggest that the number of women in most areas of science has continued to grow, in fits and starts, over the past half century. Nonetheless, quantitative surveys and individual stories indicate that the gender gap—in terms of opportunities, salaries, and career advancement—remains a challenge that needs to be addressed.